How far is climate change linked recent flooding in the UK

This morning’s
Times claims new research says the increase in flooding in
Britain in recent times is due to urban expansion and population
growth, rather than climate change.

According to the piece, this “does not agree” with
warnings from scientists that climate change can be linked to
recent flooding. But a quick look at the science shows a
combination of land use and climate change is upping the risk of
flooding in the UK.

“Misquote”

The Times story is based on a new
study from the University of Southampton. The number
of reported flooding events in the UK grew between 1884 to 2013,
according to the research.

But although the number of reported floods went up, it’s mainly
down to more people being exposed, the authors tell us. During that
time, the population grew from 38.2 to 59.1 million.

If you remove the effect of population rise, there’s
no clear increase in the number of reported flooding events, the
report suggests. This is presumably where the Times draws its
conclusion that the new research “rules out a link
between last year’s winter flooding and climate
change”.

But the authors say this is not what they found.
Andrew Stevens, co-author on the research tells us:

“[Our] work does not
rule out a link between last year’s winter flooding and climate
change as we did not look at physical data on the storms nor focus
on any specific events. That is a misquote … We must be clear [our
work] does not rule out climate change as a driver of flood
risk”.

An important distinction is between the number
of floods that get reported and how the risk of flooding is
changing. The Southampton study looks at the first of those, not
the second.

If you want to find out all the things affecting
flood risk in the UK, the latest
report from the Intergovernmental
Panel on Climate Change (IPCC) is a good place to start.

Getting wetter

The IPCC expect a warmer atmosphere to lead to
more extreme rainfall. On a national scale, there’s already
evidence heavy rainfall events are
getting more frequent in the UK due to
climate change.

A recent
study suggested the probability of seeing an
extremely wet winter like we did this year is
25 per cent higher than it was before humans
started influencing the climate.

Looking ahead, the image below shows the UK
getting about 10 per cent more rainfall on average per year by 2100
(right) compared to 1986-2005 (left).

The UK is set to see about a 10 per cent rise in
annual average rainfall by 2100 (right) compared to the period
1985-2005 (left). Source: IPCC 5th Assessment Report
Sumary for Policymakers (p20).

There’s more to flooding than just heavy
rainfall, however. So far there isn’t a clear pattern linking
climate change to greater incidence of flooding on a global scale,
according to the IPCC report.

But the picture in the UK is clearer. Scientists
are confident a lot of rain falling in a short space of time raises
flood risk, and the odds of that happening are increasing as the
climate warms. As professor Richard Allan from Reading University
told us
recently:

“[W]henever we have
heavy (and prolonged) rainfall events in the future, we can expect
them to be more intense – along with the risk of
flooding.”

A growing population

While scientists are confident heavier rainfall
and sea level rise creates a
greater risk of flooding, the biggest factor
influencing the scale of damages will be a growing
population.

According to one
study, a combination of high emissions and
population rise would expose an additional 250,000 to 400,000
people in Europe to river flooding by 2080 and potentially up to
5.5 million per year to coastal flooding.

The UK government’s
Foresight Programme estimated three to four
degrees warming above pre-industrial levels together with
population change and concentrating people and assets in vulnerable
areas could increase flood damage costs from 0.1 to 0.4 per cent of
GDP.

The choices we make about land use can increase
the flood risk too. Building on floodplains is a big problem, for
example.

The government’s climate change advisor, the
Committee on Climate Change (CCC),
found in 2012 that England’s floodplains
have seen more property development than other areas over the past
ten years – and one in five of those properties is at risk of
flooding.

Between 2001 and 2011,
200,000 homes were built in floodplains –
and since the government came in, changes to planning regulations
have made building in vulnerable areas easier.

Building on floodplains increases flood risk, the
Committee on Climate Change warns.

Low natural drainage

Paving over soil could be exacerbating the
problem, because rainwater is falling on concrete
rather than being soaked up by the ground. The IPCC report
highlights why soil is so important for keeping flood waters at
bay, especially in urban areas. It says:

“Maintaining soil water
retention capacity … contributes to reduce risks of flooding as
soil organic matter absorbs up to twenty times its weight in
water”

Preserving or developing natural drainage –
which involves taking
advantage of trees, plants and soil to manage
where water flows and gets absorbed – can help prevent
floods.

Resilience building

Adaptation measures to increase our resilience
to extreme rainfall and flooding can make a difference by
bolstering coastal defences, for example.
But emissions will also need to come down to limit the extent of
future risk.

In the meantime, recent events
demonstrate the risks of not being prepared for these events when
they strike.

————

Update 20th Aug 2014 14:40pm: Since publication of
this blog The Times piece updated its article, removing the text
saying author Derek Clarke had “ruled out a link between last
winter’s devastating floods and climate change. However, the Met
Office does not agree”.